1. Field of the Invention
This invention relates generally to mixing devices, and more particularly to a gas-induced mixing device used for the purpose of aerating and agitating a liquid.
2. Description of Related Art
Water, sewage and industrial waste treatment are becoming crucially important in today's ever increasing population. They are also becoming extremely expensive processes, as more and more treatment is required. As such, new treatment means are continually being sought, for improved efficiency and economy in this industry. Aeration and agitation is an integral part of these treatment processes.
The following art defines the present state of this field:
Clough, Jr., U.S. Pat. No. 3,788,616, teaches a "system for simultaneously aerating and agitating a body of liquid. The system comprises a body that is pivotally mounted in the liquid with its pivot point located intermediate its ends, and means for feeding air to the lower side of the body. The body is adapted to trap alternately at each end sufficient air to cause that end to rise in the liquid, and means are provided for releasing the air trapped at each end of the body when that end has risen a predetermined amount, with the result that the body oscillates on its pivot axis in see-saw fashion".
Everett, U.S. Pat. No. 4,363,212, teaches a "buoyancy prime mover that converts the potential energy of a gas buoyant within a liquid into rotating mechanical energy comprises a plurality of rigid or collapsible buckets joined by one or more chains with rotatable sprockets and shafts to form a continuous loop so that when the buoyant gas is trapped within the buckets, the buckets rise through the liquid and rotate the chain and sprockets to generate power".
Parks, U.S. Pat. No. 4,595,296, teaches an invention which "relates to a mixing and blending system in which pulsed air or gas bubbles of predetermined variable size and frequency are injected into a tank containing materials to be agitated or stirred for mixing or blending. The air introduced at the bottom of the tank through an air inlet opening. There may be more than one air inlet and the inlets may be provided with accumulator plates depending upon diameter and height of the tank in which the mixing and blending is taking place. The inlets are located so as to create circular torroidal flow of fluid in a generally vertical plane. The accumulator plate has the purpose of assisting the formation of essentially a single bubble from the compressed air charge made to the air inlet and increasing the time required for the bubble to rise through the liquid by causing it to be formed more quickly and closer to the bottom of the tank. Hence, the accumulator plate is utilized in low viscosity liquids such as water".
Hjort, et al, U.S. Pat. No. 4,779,990, teaches an "impeller apparatus for dispersing a gas into a liquid in a vessel includes a centrifugal flow turbine, the blades of which are formed with a substantially streamlined trailing surface terminated by a sharply pronounced spine. The blade is formed by a plate-like initial blank being cut to a shape having a central line of symmetry, the blank then being folded along the straight line of symmetry.
Litz, et al, U.S. Pat. No. 4,919,849, teaches a "gas-liquid mixing process and apparatus having a vessel with an axial flow down-pumping impeller in a draft tube has gas ingestion tubes extending into a body of liquid from a hollow portion of the impeller shaft or other fluid communication means with the overhead gas in the vessel. Upon gas-liquid mixing at liquid levels that interfere with vortex development by the impeller, gas is drawn from the overhead through the ingestion tubes into the body of liquid".
Small, U.S. Pat. No. 5,156,788, teaches a "device for use in the mixing of fluids, e.g. the gasification of liquids, comprises an elongate member including an internal passage; and, mounted on the elongate member via radial arms, one or more venturi members each having a convergent-divergent duct whose axis is substantially tangential to the elongate member, and in which the neck of the duct has an opening in communication, via passages in the radial, with the internal passage. On rotation of the device, reduced pressure in the duct neck draws fluid down the shaft of the elongate member".
Middleton, et al, U.S. Pat. No. 5,198,156, teaches a "turbine agitator assembly including a reservoir for liquid, a rotor mounted in the reservoir and with a plurality of radially extending blades, and sparger means for introducing a fluid into liquid in the reservoir. The fluid sparger means and the rotor are so constructed and arranged that, in use, the rotor blades (submerged in the liquid) and/or the liquid flow they generate disperse the sparged fluid. Each of the blades is hollow and has a discontinuous leading edge, only a single trailing edge along an acute angle, no external concave surface and an open radially outer end".
The prior art teaches a variety of means of mixing liquids such as turbines, rotors with blades and other various mechanical devices as well as gas-induced mixing. However, the prior art does not teach a light-weight, mixing device which traps gas bubbles naturally evolved within the liquid, nor one that uses this gas or an induced gas stream to provide the needed mixing. The prior art teaches a non-motorized gas-induced mixing apparatus where gas bubbles are used to aerate and agitate a liquid, and it teaches a non-motorized gas-induced mixing apparatus which uses the gas bubbles as an impetus to move a component through the liquid in order to agitate it as well. The present invention is an improvement on these devices providing advantages in efficiency, control and effectiveness. It fulfills these needs and provides further related advantages as described in the following summary.